Mr Brodie said last night he paid Ms Wilson as “outsourced contract staff” to do constituency casework and arrange meetings for him.

However, Ms Wilson described herself in Companies House filings as “unemployed (ex-civil service)” for the entire period when the payments were made.

The amounts paid were up to 85 per cent higher than those allowed for staff by the Westminster parliamentary expenses watchdog, Ipsa.

"At the very least, we need an urgent investigation by the authorities, and full disclosure from the SNP"

John Lamont, the Scottish Conservative chief whip

The sums do not appear in Companies House filings and none of them have been declared by Ms Wilson in her register of declarations.

The arrangement is unusual. Almost all other MSPs’ staff are employed and paid directly by the parliament, not as contractors.

At least £20,000 of the money was paid during the 2014 independence referendum campaign and £20,000 during Ms Wilson’s bid to become an MP.

Caledonii Resources was set up by Ms Wilson, then an SNP candidate on South Ayrshire council, in April 2012. She was elected a councillor the following month.Almost at once, according to Scottish Parliament records, it received two payments totalling £4,464 from Mr Brodie. Four-figure sums were paid most months for the next three years.

Corri Wilson is the SNP MP for Ayr, Carrick and Cumnock

MSPs are allowed to use contract staff but only a handful do so and for much smaller sums. In 2014/15, more than 60% of all money paid to MSPs for contract staff was claimed by Mr Brodie and went to Caledonii Resources.

Breakdowns submitted to the parliament show that in August 2014 alone, in the run-up to the referendum, the firm was paid £2,501.60 for 154.5 hours’ work, a rate of £16.19 an hour.

Permitted rates for Scottish Parliament staff are not published. However, under Ipsa rules, a caseworker based outside London at the time could only be paid from £8.79 to £13.87 an hour and a senior caseworker between £10.44 and £15.53 an hour.

John Lamont, the Scottish Conservative chief whip, said: “The evidence here suggests that one SNP politician has been milking the public purse in order to pass on cash to a fellow SNP colleague. At the very least, we need an urgent investigation by the authorities, and full disclosure from the SNP.

“For the party to fail to respond to questions on this is appalling. As always with the SNP, they complain the loudest about imagined grievances, but then shut up shop when it comes to themselves.”

An SNP spokesperson said: “All MSPs require staffing to support their work for constituents, including undertaking casework and administrative duties. Both Chic Brodie and Corri Wilson have acted entirely in line with parliamentary rules."